1. Field of the Invention
The present invention relates to a pneumatic tire, and in particular, it relates to a pneumatic tire in which thin grooves are formed in a land part of a tread surface.
2. Description of the Related Art
In a pneumatic tire in which a land part such as a block and a rib is provided in a tread part, it has hitherto been known to provide the land part with a sipe extending in a tire width direction for the purpose of enhancing drainage properties or the like.
For the purpose of enhancing a water removal effect within a ground contact plane by sipes, JP-A-10-86612 discloses that the thickness of the sipe is alternately varied large and small along a longitudinal direction of the sipe. For the purpose of enhancing the block rigidity without impairing an edge effect by sipes, JP-A-2005-67274 discloses that a raised bottom part by plural tie bars provided at intervals in a sipe length direction is formed in a bottom part of the sipe, thereby varying a height of the raised bottom part. For the purpose of enhancing a wet performance by sipes, JP-A-7-276923 discloses that not only a water draining recess is provided on one lateral face of the sipe, but also a linear water cutting edge is provided on the opposing lateral face thereto.
In a pneumatic tire in which a land part partitioned by main transverse grooves extending in a direction intersecting with a tire circumferential direction is provided in a tread part, when the rigidity of the land part is high, a vibration sound (also called a “block vibration sound”) of the land part generated from the main transverse grooves, or uneven wear such as heel-and-toe wear is generated. Though the rigidity of the land part can be reduced by providing a sipe in the land part, it may not always be said that such is sufficient, and it may not be said that the rigidity of the land part can be sufficiently reduced even by the sipe configurations described in the foregoing JP-A-10-86612, JP-A-2005-67274 and JP-A-7-276923.
In order to sufficiently reduce the rigidity of the land part, it is effective to provide a thin groove having a groove width that is narrower than the main transverse grooves but wider than the sipe. However, when the thin groove having a groove width wider than the sipe is provided, a resonance sound from the thin groove is easily generated, and an effect for improving a pattern noise performance becomes insufficient.